ClamAV versions 0.93.3 and prior contain a vulnerability that could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition.
The vulnerability is due to a memory handling error when handling .chm files. An unauthenticated, remote attacker could exploit the vulnerability by sending a crafted .chm file to a system that uses ClamAV to scan for malicious code. When processed, the .chm file could cause ClamAV to crash.
ClamAV has confirmed the vulnerability and released updated software.
Indicators of Compromise
ClamAV versions prior to 0.94 are vulnerable.
The vulnerability is due to an invalid memory access error by libclamav/chmunpack.c when handling .chm files. An unauthenticated, remote attacker could exploit the vulnerability by sending a crafted .chm file to a system that uses ClamAV to scan for malicious code. When processed, the .chm file could cause ClamAV to become unresponsive or fail, resulting in a DoS condition.
Systems most at risk are those that use ClamAV to scan files from external e-mail messages. In this instance, the attacker could exploit this vulnerability by sending an e-mail message containing a malicious .chm attachment to the target system. An attacker could take advantage of the failure of the ClamAV application to attempt to send malicious software to a system while it is unprotected.
Administrators are advised to apply the appropriate updates.
Administrators are advised to configure ClamAV to restart in the event of an application crash.
Users are advised not to download files from untrusted sources.
Administrators may consider using a mail gateway that implements file scanning with an application other than ClamAV in order to block malicious e-mail attachments at the network perimeter.
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Cisco Multivendor Vulnerability Alerts respond to vulnerabilities identified in third-party vendors' products. These alerts contain information compiled from diverse sources and provide comprehensive technical descriptions, objective analytical assessments, workarounds and practical safeguards, and links to vendor advisories and patches.